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Dw D. A. CHRISTIAN 38,564

TELEPHONE SYSTEM Filed'APril 1, 1929 5 sheets-sheet 1 Fig. I.

David Edam 5km Dec. 10, 1929. D. A. CHRISTIAN 1,738,554

- TELEPHONE SYSTEM Filed April 1929 5 Shets-Sheet 2 Fig. 2.

' Imm David 5:1 am Ehms 1am I 10, 1929., D.'A. CHRISTIAN 5 TELEPHONE SYSTEM Filed April 1, 1929 5 Sheets-Sheet 3 23 5 2 fill 1 1 1 3 2 i Inna-mint David Hdam CI'TIEHEI Dec. 10; 1929. D. A. CHRISTIIAN 1,733,564

TELEPHONE sysTEM Filed April 1, 1929 5 Sheets-Sheet 4 s Fig. 4.

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I Inuantar David Hclam CI'LFTFHET.

Dec. 10, 1929. 11 cHR|$T|AN 1,738,564

TELEPHONE SYSTEM Filed April- 1929 5 Sheets-Sheet 5 llllll Fig.5.

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ZM ccc Z OSW- kl: VM R Imam David Fldam [I'm Patented ec. 10, 1929 DAVID ADAM CHRISTIAN, OF LONDON, ENGLAND, ASSIGNOR T SIEMENS BROTHERS & COMPANY LIMITED, OF LONDON, ENGLAND TELEPHONE SYSTEM Application filed April 1, 1929, Serial No 351,487, and in Great Britain February 25, 1928.

by dialled impulses. To avoid the difi'iculty that on an interparty call exchange apparatus common to a number of lines may be held unnecessarily, arrangements have been proposed to release exchange apparatus such as first selectors and to mark a line engaged- 1f dialled nnpulses do not arrive 1n a predetermined, period of time.

Whilst these arrangements serve the purpose in view, they do not distinguish between an interparty call and a permanent loop or line fault giving the calling condition.

The present invention has in View imiroved arrangements for providing for a throw-out of exchange apparatus normally seized in the case or" a call between parties. An engaged marking may also be placed on the line.

In the present invention a subscriber desiring to call a party connected to his party line first dials a special number and then proceeds to call by his hand generator or other signalling means.

The effect of dialling the special number is to cause the exchange apparatus used in common to disconnect itself from the party 1 line and to procure the sending of a signal to equipment individual to the party line which thereupon operates to prevent further common apparatus being seized. At the same time the individual equipment may provide for the placing. of an engaged marking on the line.

The signal may be sent from an exchange selector or from a register-sender if the system employs the latter and obviously will 'only be sent if the selector or register has been set in accordance with the prescribed number.

The individual equipment receiving the signal may on operating provide for the holdmg of th cut off relay usually provlded which would normally release on disconnection of the apparatus used in common so that further common apparatus is not seized. Such cut oil relay would be held operated so long as the calling condition of the line continued.

Using the method described for dealing with inter-party calls, permanent loops or line faults giving the calling condition may be dealt with by the method involving nonreceipt of impulses Within a measured time.

In the case of rural party lines simplex dialling is generally employed and the party line, where it enters the exchange, is connected to a transmission bridge forming part of the line equipment. For the engaged mar ring in the case of an interparty call, we may provide in the line equipment a relay the circuit of which is made at the common exchange apparatus when the special number is dialled and this relay when operated may be locked up in a circuit including make contacts of the line relay on the incoming side of the transmission bridge or contacts of a relay controlled by the said line relays. The relay which is so locked up may be used to apply an engaged marking to the test or private wire of the line and at the same time complete a holding circuit for the test and cut-otl' relay of the line which relay is already operated consequent on access being given to the common exchange apparatus by the preselector of the line or by a finder switch.

In these circumstances the line equipment is in the condition taken up on an incoming call and the disconnection of the common exchange apparatus and the former holding circuit for the test and cut-ofl relay is Without effect.

Since only a signal has to be passed back from the common exchange apparatus to the relay aforesaid, the disconnection of the apparatus may be directly due to the apparatus being brought to a prescribed position, slow release relays providing for the slight delay sufficient to cause the signal to be effective. The signal circuit may be entirely separate from the speaking and test circuits. It maybe noted that the method above described in which a special number is dialled allows the normal use of a dialling signal and disconnection thereof when a train of impulses has been dialled.

Line faults may be dealt with as follows An additional line relay is provided on the outgoing side of the transmission bridge and a cut-off relay to disconnect the same from the line. A slow release guard relay is also provided,'thecircuit ofwhich is made when the cut-oil relay'operates.

This guard relay operating, prepares a holding circuit for itself including one of its make contacts and a make contact of theline relay. If there is a fault on the line and by suitable arrangcment-thetest wire'is opened attheseized exchange apparatus aftera pre scribed intervahthe cut-off relay will release and're-connect theline relaybefore the guard relayc-an release. IIt'therefore will be held dependent on the line relay being operated andimayihold openastarting circuit for a finder or a preselector to prevent further seizure; and-also-close an alarm circuit.

Reference will-now beimade to 'the accompanying drawings which show by way of example anapplicationof the invention to a systemto which connections are'ordinarily setup Iovera connecting circuit under the control of a register controller or operator circuit temporarily associated therewith. For calls betweenpart-ies on-the same line the calling'party rings the called party direct by means of a hand generatorin accordance with a predetermined code.

Figure 1 shows auxiliaryapparatus connectedtoparty lines between themain distributing fr-ame-and the multiple; Figure 2, which should-beplaced to theright of Figure 1,-shows a subscribers line circuit and. Figure 3, 'which-should-be placed to-the right of Figurez2 shows a connecting circuit. Figure 4; Which-should berpl-aced beneath Figure 3, and Fig. 5, which shouldbeplacedtothe right ofFig. 4,-show an operator circuitfor setting up calls between two-subscribers.

A brief outline of the operation of the sys-. tem will'first begiven followed byadescription in greater detail of the various circuit operations.

When a subscriber originates a call a signal isgiven toa'n assignor-which has one of two operator circuits preselected and the starting circuit of-thepresclected operator, if idle, is closed.

Alinkfinder DF which also acts as a sequence switchis-startedin search of a free connecting'circuit to the ends of which are connected'a call seeker DS and a connector DC. An-idle connecting circuit having been found, the call seeker is started in search of the callingFlineitoconnect itto the operator. Dialledimpulsesfrom the calling subscribers dial take effect on-a two-motion recording switch RS which is stepped vertically in accordance with the first digit and in a rotary direction in accordance with the second digit of a two digit number. When the number has been recorded the two-motion switch is stepped further, interacting with the driving magnet of the connector until a limiting or home position is reached, the connector being simultaneously stepped. It is arranged that the number of further steps taken by the recording switch added to the number representing its position in the bank makes up a given number. Consequently, the connector is stepped by a single impulse train over a number of contacts corresponding to the complement of the dialled number and is thusset on to the contacts of the wanted line if the connector multiple is suitably arranged.

The link is tested in the usual manner, and if free the connection is switched through and theoperator circuit freed for further use.

Arrangements are provided for the purpose of code ringing'rural party lines.

The link finder serves as a sequence switch to connect in circuit the operating magnets of the call seeker and connector and to connect the ringing current to the called line each at the appropriatetime.

Referring to-Figure 1, the auxiliary apparatus connected to the lines of party line subscribers includesa repeating coil with'a line relay AA connected between battery andthe two line wires. It is assumed that impulses fromthe subscribers dial will be transmitted overia simplex circuit asis usual with-such lines. To the exchange side of the repeating coil is connected a relay S for cutting out'the repeating coil while a party line subscriber isbeing rung. Relay LC is operated consequent onthe receipt in the operator circuit of a special digit denoting an interp'arty call and locks up under control of relay AV. Relay-LO connects earth to the test Wire of the subscribers line to hold the cut off relay and tomark the line engaged in the banks of the connecting switches.

In Figure 2 is shown the line circuit which comprises'aline relay L, acut off relay CC andrelay PG, the function of which is to deal with faults-on the line resulting in a line continuing in a calling condition. In the-lower part of the figure is shown an as signor common .to a number of lines and comprises three relays A, B and C.

WVhena partyline subscriber lifts the receiver to call, a simple:\' circuit is formed current flowing to both line wires from theearthed positive pole ofbattery through the bell coils ofhe subscribers instrument, and relay AA operates Contact an operates relay AV and contact (m short circuits the condenser connected to the exchange side of the repeating coil thereby providing a loop over which relay It operates. Contact Z connects battery over relay CO via contact pg to the test Wire 0 connected to the test bank contact of the call seeker DS, Figure 3, to mark the line as a calling line. Contact Z connects earth over contact p to relay A in the assignor. This circuit is as follows :earth over contacts P, 179 cl, bl, winding 1 of relay A, contact 6 to battery. Relay A operates and at contact a connects winding 1 of relay B to earth. Relay B does not operate however, as it is short circuited. Contact a closes to hold relay A against operation of relay B and contact a closes a circuit from earth on the common con- 7 nection from the line circuit over contact 64 and winding 1 of relay C to battery.

Relay C operates and opens contact there by permitting relay B to operate by means of its winding 1 in series with winding 10f relay A.

Contacts 6 and 6 do nothing as contact 0 is open and there is no circuit over windings f relays A and B. Contact 5 opening leaves relays A an l B operated dependent releases.

held by means of their windings 1.

on contact a and contact b opens the circuit of winding 1 of relay C. 11 operator No. 2 is engaged the circuit over wire OSl V and the front contact a will be open and relay C Contact 0 falling back closes circuits in parallel for windings 2 0rrelays A and B, relay B holdsover its contacts 5 and 6 already operated and relay A releases as its two windings oppose one another.

Relay A releasing contact aopens to prevent operation of the relay by its winding 2. Contact of falling heel: and contact 5 being in its front position relay C again operates and tests operator No. 1 over Lack contact a If operator No. 1 is tree relay C. l10l( s from battery connected in the operator circuit over wire OSl/V back contact a contact 0 winding 2 of the relay, and contacts 395 and Z A signal is thus transmitted to the operator to start to perform its functions. Contact 0 opening, relay B releases and opens the circuit of winding 1 of relay C Relay C continues to hold until the calling line has been found .by the call seeker of the connecting circuit taken into use by the operator.

It operator ilo. 2 had been free when test-er relay C would have remained held by its sec- 0nd winding and relays A and B would be When the calling line is found in this case relays A and B do not release but when another line calls relay B is held operated ver its winding 2, and winding 2 of relay A energizing i allel therewith the latter relay relerxoperator No. 1 is tested as above described.

hen the calling line is found by the call seeker of the link-circuit taken into use by the assigned operator circuit, relay CC operates to earth connected over the test wiper of the call seeker and wire 0 and locks thereto over its contact c0=.' Contact 00 disconnects relay L from the cal ing line and contact 00'' operates relay PG. j

The operation of this relay and the release of relay L opens the assignor circuit and the starting circuit of the operator.

Dialled impulses are repeated at contact as to the impulse relay in the associated operator circuit.

If the call is an interparty one a special one digit number is dialled which results in a battery connection to wire m being made in the operator circuit and relay LC is operated by means of its winding 1. This relay locks up by means of its winding 2 over contacts L0 and ac and at contact Z0 connects earth to wir'e'c. As a further result of dialling the special digit the operator circuit is released and the ordinary holding circuit of relay CO is opened, but the cut-off relay remains held over contact Z0 over which earth is connected to mark the line engaged in the subscribers multiple.

In the case of a call completed through the exchangers ay CC releases when either party clears. In the case of an interparty call when both parties have replaced their receivers relay AA releases and releases relayAV which in turn releases relay LO. Contact Z0 openrelay CC releases and the engaged marking is removed from the multiple.

lVhen relay CC operated contact co 'closed a' circuit for relay PC which operated. Whilst a call is inprogress relay CO remains operated and relay L is cut off the line so that there is no circuit over contact 229 for alarm relav PL.

Should a line fault develop and result in an operator circuit being taken into use relays AA, L, CC and PG operate as for a calling line and after a. prescribed interval, should the operator circuit seized be still held, relay CC is released in a manner to be de scribed later. Relay L thereupon re-operates and relay PG remains held over contacts Z and 399 A circuit is closed from battery over relay CO, contact Z and p9 and relay PL, the latter relay operating and closing an alarm circuit. The line is prevented from connection with the exchange so long as the calling condition persists.

In the case of an incoming call relay CC operates in series with the test relay for the connector. cuts relay L oil" the line and oper-' ates relay PG. \Vhen the code ringing gener- 1 ator is applied to ring the called line, battery is connected to the a Wire and relay S operates over contacts (m and on).

Contact 8 connects the subscribers a wire to a suitable return circuit and the ringing current is sent out over the 6 wire and front contact 8 Contact 8 disconnects the eX- change side of the repeating coil from the Z) wire. Relay S releases during the interval between successive applications of the ringingcode. When the called subscriber lifts his receiver to reply relay AA operates in an interval between successive applications of the, ringing code and contact at! disconnects relay Sand loops. the line to the exchange operating the ring tripping: relay in'the operator circuit which effects the switching through of the connection.

Referring to Figure 3 the connectingxcircuit comprises a call seeker DS and a connector .DC, the stepping magnets of which are denoted by DSM and DCM respectively. TC is-the test relay of the call seeker which is'of the typein which the wipers after use remain in the position in-which they were lastuused. The call seeker is provided with l wipers and banksywipers A and B being the speaking wire'wipers. C the test wiper and M the meteringwiper. A meteris provided for ordinary subscribers lines but in the case of party lines the bank contacts of wiper'M are connected to relayLO in the subscribers auxiliary apparatus. The connector is a single motion switch of the homing type provided with 5 wipers and banks, Wipers A 'and B? being in'the speaking circuit, C being the test wiper andD the homing wiper.

Current during'conversation is fed tothe calling line over relay LA and to the called line over relay LY. LV is a switching relay. In the designation of the wires to the contacts in the banks of the connecting circuit finder at the foot of the figure the index numeral represents the position ofthe wiper on the successive contacts associated with a connecting circuit over which the wire is first used.

Figures 4 and 5 show the operator circuit. The operator circuit has associated with it a finder DF the function of which is to search for an idle'connecting circuit. Its stepping magnet is designated DFM.

Three consecutive contacts in its banks are associated withthe sameconnecting circuit. Overt-he first of these contacts the test for a free connecting circuit is'made and the driving magnet of the call seeker is operated. IVhen the calling line is-foundthe link finder is stepped to the second of the 3' contacts associated with the particular connecting circuit. In this position impulses from the calling subscribers dials are repeated to the magnets of a two-motion recording switch RS, the wipers of which are set in accordance with the two digits representing the number of the called subscribers lines. Switch RS is pro vided with 2 sets of wipers and banks X and Y and is operated by a-vertical magnet VM, and a rotary magnet RM. A release magnet ZM is provided andalso a magnet RZM which releases A the wipers as regards their rotary motion only. The connectormagnet DCM, Figure 3, is operated in thesecond position of the link finder by interaction with magnet RM of the recording switchuntil the desired line is reached whereupon a test-of the line is made by relay'P and if it is'free the link finder-moves to the third set of contacts asso ciated with the particular connecting circuit and ringing current is connectedto the called line. 'Ringitri'pping relayTR is inclu ded in theringingbircuit and operates when the called subscriberreplies, to close the circuit of switching relay LV.

In the operator circuit ST'is the starting relay, Tv the test relay for the linkfinder, and P the test relay for the connector. A issthe impulse relay, V the release relay, D the dialling relay which determines the end of an impulse'train and Ga steering relay which connects in circuit the appropriate operating magnet of" the recording switch RS. PS and PT are relays concerned with-the. release, as far as rotary motion is concerned, of switch RS during its interaction with the connector driving magnet and Q is a relay which limit-s the stepping of switch RS in its transmission of impulses for the setting of the connector. Relay BL is concerned with therelease of the operator and connecting circuits during interparty calls. The function of other relays will be clear from thefollowing description which will coverthe operation of the finder and connecting circuit Figures 3, 4 and 5 being taken together.

\Vhenthe assignor receives a signal from a line circuit-that a. call has been originated, earth is connected tothe operator circuit starting wire OS'VV which extends over vertical off-normal contact ic of switch RS, contacts d ,'t1"* and relay ST to battery. Relay ST operates and at contact st prepares the circuit of the link finder test relay T. Contact st starts a motor driving the interrupters and ringing generator and cams. Contact st connects earth over an interrupter and back contact t to magnet DFM which operates and steps thewipers of the link'finder in searth of a free connecting circuit, a free connecting circuit being denoted by battery potential on wire 1 connected in the bank of wiper 1 of switch DF. WVhen such a contact is encountered, relay T operates in a circuit from earth over contact 825 its high and low resistance windings in series, wiper 1 and bank contact, wire 1 wiperE of connector DC in its normal position, bank contact, contact te of relay TC, contact Z12 resistance to battery. Contact t disconnects magnet DFM from the interrupter and the finder comes to rest. Contact t short circuits the high resistance winding of relay T to mark the connecting circuit engaged and contact 15 prepares the test circuitof the call seeker of the seized connecting circuit. Contact #0011- nects an earthed interrupter over back contact p wiper 5 of switch DF on the first contact associated with the seized connectingcircuit, wire 5 contact $0 magnet DSM to battery. MagnetDSM operates and rotates the wipers of the call seeker in search of the calling line which is marked by the connection of battery over the cut-off relay in the line circuit to the bank of wiper C YVhen the contacts connected with the calling line are rectly to wiper C to mark the line engaged to party line subscriber.

connectors of other connecting circuits and to,

hold the connection. Contact to opens the call seeker driving magnet circuit. Relay B operates over contact t wiper 8., wire 8 front contact 250 normal contact and Wiper R wire 1 wiper 1, lo v resistance winding of relay T, contacts 6 and 525 to earth. Contacts 6 and 5 connect the incoming speaking wires over wipers A B contacts to and wires 3 and 4 ipers 3 and 4 of switch DF torelay A. Contact 6 connects earth over front contact t to magnet DFM and the magnet attracts its armature. Relay A operating thecircuit of relay V is closed at contact a and relayV operates and closes a holding circuit for relay B over cont-acts o za and rl Meanwhile relay CU has operated in the line circuit and released relay Land the starting circuit has been opened at the assignor. Relay SEQ-thereupon releases and releases relay T. Contact i falling back opens the circuit ott'magnet DFM, contact 86 b this time being open, and the connecting circuit finder wipers are stepped to their second position. Inthis condition relay TC remains held over front contact 00 wire 8 wiper 1 tcearth connected thereto by contacto Further results of the operation of relayV are the operation of relay I) in a circuit over contact got a (operated) 7: 10 W; the preparation of the circuit of the rst-of a pair ofslow alarm relays SA at contact '0 and the maintenance of tie motor starting circuit at contact 12 Relay D operating prepares a holding circuit for itself during impulsing at contact- (Z and at contact (Z connects dialling signal over wire DSKV and contact to the incoming line. Contact (Z prepares the circuit of vertical magnet VM and contact (Z opens the starting circuit to prevent seizure by another calling. line.

[ The subscriber hearing the dialling signal commences to dial the wanted subscribers number which consists of twodigits for an ordinary subscriber and three digits for a It will first be assumed that the wanted subscriber is an ordi nary subscriber and not one on a rural party line. Dialled impulses are received by relay A and are repeated over contacts (R, (Z 9 to the vertical magnet VM. Contact a in its back )OSIllZlOll closes the holding circuit'of relay D. i

r-itthe first vertical step the vertical offnormal contacts 70 ,10 0 and k are operated. The first of these contacts when operated holds open the starting circuit preventing further seizure of the circuit while switch RS is away from its normal position. Contact 70 prepares a circuit for relay G which operates at the end of the first train of impulses and contact 70 disconnects dialling signal. The wipers of switch RS are stepped vertically in accordance; with the first digit dialled and at the end of the impulse train, relay A remaining operated, relay D releases and at contact d the following circuit is closed; earth over contacts v 10 k p8 d 7 relay G to battery. 7

Relay G operates and at contact g closes a circuit as follows Earth over contacts 41 Q0 9 a 176 relay D to battery. I

Relay D operates and at contact d closes a holding circuit for relay G over contacts 9 and 12 Contact 9 connects the rotary magnet RM in place of the vertical magnet VM. Contact d disconnects relay Q, from the rotary magnet and contact d opens to delay the operation of relay E. The second train of dialled impulses is repeated over contacts a (Z 9 298 to the rotary'magnet which steps the wipers round the level. At the first rotary movement rotary off-normal contacts w w and Q0 are operated and at the end of the train the circuit of relay D now being open, that relay releases and a circuit is closed for relay E over contacts (Z e0 and 0*. Relay G releases. Relay E operates and closes a circuit from earth over armature contact 620m of the connector magnet, wire7 wiper 7 in its second position, contacts 6 p 9 d 198 magnet RM to the battery. Magnet RM operates and advances its wipers one step. Towards the end of its stroke armature contact rm closes and magnet DCM of the connector operates over wire 6 wiper 6, front contact e and contact rm and towards the end of its stroke opens its armature contact dcm releasing magnet RM. The armature of magnet RM falling back contact rm opens the circuit of magnet DCM which thereupon releases and advances the wipers of the connector one step into the bank. Magnet RM continues to step, interacting with the connector magnet until the tenth contact in the level is reached.

A limiting or home position is provided on the recording switch to limit the stepping of the switch and of the connector. This position is such that when the recording switch is set by dialled impulses to the first contact in the first level, the subsequent stepping of lines connected to its banks, the limiting position on the recording switch will be the tenth contact in the fifth level. This may readily be ascertainedif it is considered that by. dialling'll, the two digit number that effects the setting of the recording switch on the first contact in the first level, the subsequent stepping by interaction over that leveliwill result'in 9 steps being taken to reach the tenth contact inthe level. The switch is then released asregards the rotary position of the wipers and'is given a vertical step and stepping continues. over'the second and sub sequent levels until contact 10 in. the fifth leveliis reached by which time the total number of steps taken by the recording switch and consequently by. the connector will be 49. It will thus be seen: that the lines in the: connector banks are numbered backwards beginning with the highest subscribers numbers, .5 9'-in the. above example and ending with: 1-1

Airelay Q, is.connected to the limiting position in thebank of' wiper X of the recording switch and a relay. PS is connected to the tenth contactzof all levels inthe same bank reached-.bythe wiper before that in which relay Q, is connected.

When the. recordingswitch is stepped to the tenth contacts of. a level other. than the limitingor home rlevelgrelay PS operates by means of its windingl over wiper X and at contact ps opens the circuit of magnet RM. A circuitis closed for. relay PT in series with windingfl of'relay. PS, contacts ps w and '0 Contact ps closes the circult of rotary releasemagnet RZM- which operates and returns thewipers to the rotary. normal position whereupon the rotary off-normal contacts are restored. Acircuit is now closed for relay PT over. contact pt and front. contact w independently oflrelay PS which releases a-fter a short interval. Meanwhile relay D re-operates in a circuit over front contacts 106 psfllcicontactsw andm and at contact 01 closes" acircuit from earth over contacts pct-dig for the vertical magnet VM. The magnet operatesandthe wipers are stepped to the next level, the magnet circuit being opened on the release of relay PS. The release ofrelay'PS' brings about the release of relayD at contact 798 and the stepping cirsuit of magnet RM is again-closed. Relay Gr re-operates and releases relay PT at contact 9 but itself is subsequently released due to the opening of contact 1.0 when the wipers are stepped by the operation-of magnet RM. Relay E holds operated during the rotary re lease and subsequent vertical step.

Interaction of the two magnets continues until the limiting position on the recording switchi's' reached whereupon on the opening of contact (lam magnet RM is held momentarily in: series with relay Q, winding Z to earthover wiper X. Relay Q operates and at c'ontactg. connects a high resistance winding 2 in the magnet circuit and the current being thereby reduced, magnet RM releases. Re-

lay Q now holds by means of its-winding2 and at contact 9 connects relayQA over front contact 6 wiper 6 and magnet DCM which releases and advances the wipers one step. The connector wipers will now be found to be set on the contacts of the wanted subscribers line.

Relay QA operates and at contact ga completes the test circuit. If the line is free relay P operates from earth'over contacts 0, ga ,.windings 2. and 1 of. relay P, wiper 8 of the switch DF,.wire 8 and wiper C of the connector to battery over the called subscribers cut off relay and short circuits its high resistance winding 2- at contact 2 thereby marking the line engaged; Operation of relay Q, opens the circuit of. relay Eat contact 9 and the slow release of relay E provides an interval for a fleeting test of the line. The subsequentrelease of relay E disconnects relay QA. Before the release of relay E however, andconsequent on the operation-ofrelay P, magnet DFM receives an impulse over contacts 6 p and e and the switch DF is stepped to its third-position.

Relay F being operatedcontacts p and 39 close the ringing circuit whichis as follows: battery over ringing generator, contacts a p e wiper 7 in position 3, wire 7 contact Z22 wiper B the called subscribers line and bell, wiper A contact; Z11 wire 6 wiper 6, contacts 6 10 00 Winding Z of relay TR to earth. The called-subscribers bell is rung and a ringing'signal'is connected to the calling line over wire RSW, contacts 711 79 d, 6

wiper 3 andcontact to.

When the called subscriber lifts his receiver to reply the. line is looped and relay TR operatesin the circuit above traced and locks by means of itswinding 2 over contacts tr and v Contact t1 operates relay LO, Fig. 1, ot er front contact 12?, wiper 5 and wire 77?. but this relay performs no useful function in this connection. Contact m connects earth to wiper 2 and relay LV operates over wire 2 and at contacts Z12 and lo 'connects earthdirectly to'wipers C and" C to mark both the calling and called lines busy to other connecting switches after the operator has been released. Contact Z11 shortcircuits relay P which thereupon releases. Current is fed to the callingline-over relay LA. and contacts 1'0 and Z0 and to the called line over relay. LY and'cont-acts Z11 andlt. I

Relay LV locks up over contacts Za and Z31 and at contact Z12 opens the circuit of relay TC which releases. Contact to falling back prepares the homing circuit of the connector. Consequent on the opening of contacts to and 60 relay A releases and at contact a releases relay V. Relay V releasing releases relay at contact 0 andrelay TR at contact 41 and contact 12 opens the circuit ofrelay SA releasing that relay should it be operated'and contact v opens the motor start circuit.

Contact "u falling back closes the circuit oi the releasemagnet ZM and the magnet operates and releases the recording switch, the

'inagnet circuit being opened by the opening of contact when the normal position is reached.

Release of the switch releases relay Q, and the starting circuit is prepared for subsequent seizure of the operator circuit by the closure of contact 70 At the end of the conversation the first subscriber to clear releases relay LV at contact Zct or Zg as the case may be. Relay LV disconnects both feed relays from the lines and removes the busy markings on the-test wipers of the connecting switches. Contact Z42 closes the homing circuit or" the connector over Wiper D and contacts to" and tZc-m and the connector is returned to normal whereupon the link finder test circuit is again prepared over wiper E in its normal position and contacts $0 and Z zfl.

Should the line when tested be found busy relay P does not operate and on the release of relay E following the operation of relay Q which determines the end of the stepping of the connector, a busy signal is transmitted to the calling subscriber over wire BSlV, contacts 9 6 9, (Z 6 wiper 3 and contact 60 When the calling subscriber hears the busy signal he replaces his receiver releasing relay A which brings about the release of the operator-as previously described.

It a call is made to a subscriber connected to another rural party an additional digit is dialled for the purpose of connecting the appropriate ringing code to the called line in place of the usual interrupted ring. For this purpose an additional bank and wiper Y is provided on the recording switch.

Contacts in the bank corresponding to party line subscribers are connected to a relay E which disconnects the ordinary ringing circuit and connects this circuit over a single motion switch DP to a code ringing cam selected by the switch DP in accordance with the additional digit.

At the end of the second train of impulses contact (Z connects relay R over the bank contact and wiper Y to earth. Relay R. operates and at contact 7 disconnects the ringing generator from the ringing connection towiper 7. Contact 1 operates relay RD over normal bank contact and wiper clp and this relay prepares a locking circuit for itself at contact Ni Contact 1' opens to delay operation of relay E, contact (i being late in closing. The third digit is now dialled and is repeated over contacts a rcl r to magnet DPM of the single motion switch. Switch DP is stepped in accordance with the third train of dialled impulses. During impulsing relay RD holds over contacts W, a and rd and at the end of the train,

7 to a code control cam CCC. This cam has a nose which when it is brought into contact with the inner spring associated with the cam, closes both the contacts and connects earth directly to relay CO over contacts 1* and 7). Relay CC operates and on the passing of the cam nose, the inner spring rests on a surface of a radius sutlicient to open the outer contact, yet maintain connection with the centre cont-act. In this position relay CC holds to earth connected overcontact 5 co During the operated period of relay CC the code ringing generator is connected over the appropriate cam, bank and wiper jcZpZ, front contacts .00 a and p and back contact 6 tothe outgoing Z) wire over wiper 7. Contact 00 disconnects winding Z of relay TR and connects battery to the a wire for the purpose of operating relay 6 in the auxiliary line equipment to bridge the repeating coil. At the end of the code ring the inner spring associated with cam CCC passes on to a surface of reduced radius and opens the circuit of relay CC which releases and connects earth over relay TB to the a wire and battery over wiper 7 to the Z) wire.

lVhen the subscriber answers the call, relay TR. operates in the interval between the end of a code and its re-commencement and eiiects switching through of the connection as for a local call. Release of relay P opens the circuit of relay CC and when the recording switch RS is released relay R releases and at contact 1* closes the homing circuit of switch DP. Magnet DFM operates and interrupting its own circuit at contact (him steps the switch to normal.

If a subscriber wishes to speak to another connected to the same line, he lifts his receiver and awaits dialling signal as in the case of a call through the exchange. On receipt of the dialling signal, the dials a single special digit, to denote that an interparty call is about to be made after which, with the receiver still off the hook, he operates the hand generator to call by mea s of a code the party required. 7

In the operator circuit shaft contact 70k of switch BS is arranged to be operated when the switch is stepped to the levelcorresponding to the special number assigned to interparty calls. The operated contacts prepare a circuit for a relay RL which is operated on the release of the dialling relay D and brings about the release'ot the operator and connecting circuits and the application of the busy marking to the subscribers line in the multiple.

When the special digit is dialled the wipers of switch: RS are brought to rest opposite the level'assigned to interparty calls and contact 7074 is operated. On the subsequent release of relay D relay RL operates over contacts (Z and Ma and locks up over contact 9" in parallel with contact d Contact TZZ opens the holding circuit of relay 9 and this relay releases releasing relay A at contacts Z2 and 5 Contact a falling back opens the circuit of relay V which re leasesafter a brief interval and at contact 12 opens a further point in the holding circuit of relay B. Contact 42 closes the circuit of the releasemagnet ZM which operates and returns switch RS to normal, the magnet circuit being opened by the restoration of the vertical off-normal contact Vifhen relay RL operated, contact r connected. battery over a resistance, back contacts 25 p wiper 5 on the second contacts of the set associated with a connecting circuit, wire 5 wiper M wire m winding Z of. relay 10 to earth. Relay LO operates and locks up dependent on relay AV which is held byrela'y AA connected to the subscribers line and at contact Z0 connects earth to wire 0 to mark the line engaged inthe multiple and to hold relay 00 after the disconnection ofthe earth on wiper C by contact Z0 consequent on the release of relay TC at contact 12 Relay BL is released by the opening of contact 7070 when release of switch RS commences.

During an interparty call although the subscribers line remains in a calling condition and the operator and connecting circuits are freed and the line marked busy in the multiples;,yetthe alarm circuit is not brought into operation as it wouldbe if the calling condition persisted owing to a line fault or to a receiver beingremoved and no impulses being dialled.

The operation of the system under line fault conditions will now be outlined.

Each operator circuit is provided with a pair of relays SA and ZA operable over a slowly rotating cam SZ. The cam after connecting earth momentarily over the right hand contact continues to rotate and after the elapse of a predetermined interval connects earth momentarily over the left hand contact. After further rotation earth is again connected over the right hand contact and another cycle of operations is commenced. The intervalbetween successive applications of earth over the right and left hand contacts is sufiicient to cover the normal period during whichan operator is in use on a call; Should this period be exceeded, as for instance, by a subscriber failing to dial within are-asonable time or by the line relay. being operated; due to a fault, the operator circuit is released.

When an operator'circuit is taken into use relaysB, A and V (Fig. 4) operate. Contact v 'connects relay SA to'the right hand contact operated by cam SZ and when earth is connected over this contact by the cam, the relay operates, locks up over contact sa andprepares a-circuit for relay ZA over con? tact sa If, by the time earth is connected to the left hand cam contact, the operator circuit has not been released relay A operates and locks up over contacts Sc and zea Contact-2a opens and releases relay B which in turn releases relays A and V and the operator circuit is released from the calling line, relays SA and ZA- releasing. Relay TC is released and earth is disconnected from wiper C and relay CO in theline circuit releases. Relay AA being still operated relay L re-operates over a loop circuit closed by contact cm and relay Pt; (Fig. 2) remains held and the alarm relay PL is operated. The line is marked unavailable to a connector by the absence of battery potential on the testbank contact.

What I claim is 1. In a telephone system, a plurality of party lines, a ,dialateach party line station, exchange apparatus common to said lines and seizedupon the initiation of any call; means responsive to the dialling of a predetermined digit by a calling subscriber for disconnecting his line from said common-apparatus and for marking the line busy, and means at the calling station for signalling another party on the same line. V V

2. In a telephone system,,party lines, automatic switching apparatus seized responsive to a call on one of said lines, a dial at the calling station for controlling said apparatus toconnect with another line, means for disconnecting said apparatus from the calling line responsive to the dialling of a predetermineddigit in case the calling subscriber desires to call another, party on the same line, and means at said calling station for signalling the desired station on the same line independent of said switching apparatus.

3. In a telephone system, a plurality of lines, automatic switching apparatus for use in connecting said lines, means responsive to a call on a line for seizing said apparatus, means for releasing said apparatus operative automatically if the calling subscriber dials a predetermined digit, and means for releasing said apparatus operative automatically if he fails to dial any digit within a predetermined time.

4. In a telephone system, a plurality of lines, automatic switching apparatus for use in connecting said lines, means responsive to a call on a line for seizing said apparatus, means for releasing said apparatus if the callingsubscriber dials a predetermined digit or if he fails to dial any digit within a predetermined time, an alarm, and means for operating said alarm in case the said apparatus is released because of failure to dial but not in case of release responsive to a predetermined digit.

5. In a telephone system, a plurality of lines, automatic switching apparatus common to said lines, means for connecting a line to 10 certain of said apparatus responsive to a call or to an abnormal condition on the line, timing means rendered effective when the line is connected, means controlled by said timing means for disconnecting the line from said apparatus in case the line is in abnormal condition, and means individual to the line for maintaining the line disconnected from said apparatus and for giving an alarm.

6. In a telephone system, a plurality of zotparty lines, a dial at each party line station, line equipment individual to each of said lines, automatic switching apparatus common to said lines and seized by one of said lines when the lineassumes a calling condition, means responsive to the dialling of a predetermined digit by a calling subscriber for releasing said apparatus and for returning a signal to said line equipment and means in said line equipment responsive to said signal for preventing further seizure of said apparatus and for marking the line busy to incoming calls.

7. In a telephone. system, a plurality of party lines, a dial at each party line station,

automatic switching apparatus common to said lines and seized by one of said lines when the line assumes a calling condition, line equipment individual to said line and including a line relay and a cut-0E relay,

means for releasing said apparatus provided dialling impulses are not received Within a predetermined period, means responsive to the release. of the common apparatus for releasing said cut-oif relay and operating said line relay to close an alarm circuit, means responsive to the dialling of a predetermined digit for releasing said apparatus and returning a signal to said line equipment, and means responsive to said signal for preventing the release of said cut-ofi' relay and the closure of said alarm circuit.

8. In a telephone system, a plurality of party lines, a dial at each party line station, automatic switching apparatus common to said lines and seized by one of said lines when the line assumes a calling condition, line equipment including a cut-off relay individual to said line, means for releasing said apparatus if dialling impulses are not received within a predetermined period, means responsive to such release of said apparatus for releasing said cut-oil relay to close an alarm circuit, means responsive to the dialling of a predetermined digit for releasing said apparatus and returning a signal to said line equipment, and a relay operated by said signal to prevent the release of said cut-ofi relay and the closure of said alarm circuit.

DAVID ADAM CHRISTIAN. 

